1. Field of the Invention
The present invention relates to a method of selectively setting a selective four-wheel drive transmission system for an all-terrain vehicle, including a front power transmission line, a rear power transmission line, and a dog clutch included in either the front or the rear power transmission line for a two-wheel drive mode or a four-wheel drive mode by controlling the dog clutch.
2. Description of the Related Art
Most conventional all-terrain vehicles are provided with a full-time four-wheel drive transmission system, and some conventional all-terrain vehicles are provided with a selective four-wheel drive a part-time four-wheel drive transmission system. Generally, the selective four-wheel drive transmission system has a front reduction gear for driving front wheels, provided with a dog clutch, and the dog clutch is operated by manual operation or by an electric actuator, such as an electric motor.
An electric dog clutch has a moving member provided with teeth, and a stationary member provided with teeth. The moving member is moved axially between an engaging position where the teeth of the moving and the stationary member are engaged and a disengaging position where the teeth of the moving and the stationary member are disengaged by an electric actuator to select either the two-wheel drive mode or the four-wheel drive mode. Manual control of a dog clutch requires heavy work. Electric control of an electric dog clutch using an electric actuator for shifting the moving member only controls the electric actuator, such as an electric motor, which involves the following problems.
(1) When changing the selective four-wheel drive transmission system from the two-wheel drive mode to the four-wheel drive mode by engaging the dog clutch, the moving member is shifted from the disengaging position to the engaging position. Sometimes, the teeth of the moving and the stationary member interfere with each other and the selective four-wheel drive transmission system cannot be smoothly changed from the two-wheel drive mode to the four-wheel drive mode.
(2) In a state where the dog clutch is engaged and the selective four-wheel drive transmission system is set for the four-wheel drive mode, sometimes, the moving member is forced away from the stationary member. If the selective four-wheel drive transmission system is operated in the four-wheel drive mode with the teeth of the dog clutch engaged incompletely, the teeth are liable to be abraded quickly or irregularly because the effective torque transmitting area of the teeth is reduced.
Accordingly, it is an object of the present invention to provide a method of controlling a selective four-wheel drive transmission system provided with a dog clutch for an all-terrain vehicle, capable of smoothly changing the selective four-wheel drive transmission from a two-wheel drive mode to a four-wheel drive mode and of constantly maintaining the dog clutch in a normally engaged state in the four-wheel drive mode.
According to the present invention, a method of controlling a selective four-wheel drive transmission system for an all-terrain vehicle, said selective four-wheel drive transmission system including a front transmission system for transmitting driving power to front wheels, a rear transmission system for transmitting driving power to rear wheels, a dog clutch including a stationary member provided with teeth and a moving member provided with teeth, and included in either the front transmission system or the rear transmission system so as to be engaged or disengaged to set the selective four-wheel drive transmission system selectively for a four-wheel drive mode or a two-wheel drive mode, an electric actuator for moving the moving member of the dog clutch between an engaging position and a disengaging position, a position sensor incorporated into the electric actuator and capable of determining a position where the moving member is situated, and a controller for controlling the electric actuator, comprises the steps of: determining a position of the moving member of the dog clutch by the position sensor; sending a position signal representing the position of the moving member of the dog clutch and provided by the position sensor to the controller; and controlling the position of the moving member of the dog clutch on the basis of the position signal by the controller.
Thus, the moving member of the dog clutch can be held correctly at the engaging position or the disengaging position, the selective four-wheel drive transmission system can be set properly for the four-wheel drive mode or the two-wheel drive mode, and torque can be properly transmitted.
It is preferable that, the electric actuator is controlled such that the moving member of the dog clutch is returned temporarily to the disengaging position and is moved again toward the engaging position when the dog clutch cannot be properly engaged when changing the selective four-wheel drive transmission system from the two-wheel drive mode to the four-wheel drive mode.
Thus, it is possible to change smoothly the selective four wheel drive transmission from the two wheel drive mode to the four wheeled mode.
It is preferable that, the electric actuator is controlled so as to force the moving member of the dog clutch to the engaging position when a position sensor detects movement of the moving member toward the disengaging position by a distance exceeding a predetermined distance in a state where the selective four-wheel drive transmission system is set for the four-wheel drive mode.
Thus, it is possible to reduce the possibility of the rapid abrasion of the teeth of the dog clutch due to reduction in the area of the torque transmitting surface of the teeth of the dog clutch.
It is preferable that, the electric actuator is controlled by a duty factor control system, and the duty factor of power supplied to the electric actuator during movement of the moving member of the dog clutch from a start position to a contact position is smaller than that of power supplied during movement of the moving member of the dog clutch from the contact position to a engaging position.
Thus, shocks on the dog clutch when the teeth of the moving and the stationary member strike against each other can be reduced, and the drive mode can be smoothly changed because the electric actuator is operated at a high duty factor after the teeth of the moving member and stationary member are engaged.